Adding a proper clean-up step for unit test file system artifacts.

Change-Id: Ia602b2359f290c4327611dc092bbcdaf28c144a2
diff --git a/core/common/src/test/java/org/onosproject/common/app/ApplicationArchiveTest.java b/core/common/src/test/java/org/onosproject/common/app/ApplicationArchiveTest.java
index 8070dfe..e1c7bfc 100644
--- a/core/common/src/test/java/org/onosproject/common/app/ApplicationArchiveTest.java
+++ b/core/common/src/test/java/org/onosproject/common/app/ApplicationArchiveTest.java
@@ -35,19 +35,20 @@
 
 public class ApplicationArchiveTest {
 
-    static final String ROOT = "/tmp/app-junit/" + new Random().nextInt() + "/foo";
+    static final String ROOT = "/tmp/app-junit/";
+    static final String STORE = ROOT + new Random().nextInt(1000) + "/foo";
 
     private ApplicationArchive aar = new ApplicationArchive();
 
     @Before
     public void setUp() {
-        aar.setRootPath(ROOT);
+        aar.setRootPath(STORE);
     }
 
     @After
     public void tearDown() throws IOException {
-        if (new File(aar.getRootPath()).exists()) {
-            Tools.removeDirectory(aar.getRootPath());
+        if (new File(ROOT).exists()) {
+            Tools.removeDirectory(ROOT);
         }
     }